*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
.box{
    height: 400px;
    display: flex;
}
.main{
    width: 400px;
    height: 400px;
    position: relative;
}
.main img{
    width: 400px;
    height: 400px;
}
.mask{
    pointer-events: none;
    display: none;
    width: 200px;
    height: 200px;
    background-color: rgba(0, 0, 0, 0.3);
    top: 0;
    left: 0;
    position: absolute;
}
.small{
    margin-left: 10px;
    width: 68px;
    height: 400px;

}
li{
    list-style: none;
    width: 68px;
    height: 68px;
    margin-bottom: 15px;
}
li img{
    width: 68px;
    height: 68px;
}
.big{
    display: none;
    margin-left: 10px;
    width: 400px;
    height: 400px;
    background-image: url(./red.jpg);
    background-size: 800px 800px;
    
}